The efficiency of centrifugal pumps, such as radial discharge centrifugal impeller pumps, is inhibited by what is called parasitic frictional drag on the pump impeller. This invention is directed to a new system for decreasing the parasitic frictional horsepower in centrifugal pumps of the closed or open impeller type. For pumps of low efficiency, this parasitic loss may amount to as much as 30% to 40% of the maximum power. Reduction of this power loss is beneficial over the entire flow range of the pump, including shut-off.
Attempts have been made to use rotating side walls for such pumps, with the side walls mounted on mechanical bearings concentric to the pump's center line. Such a rotating wall must be made structurally massive to support the pressure differentials between the front and back of the rotating walls. Furthermore, such a rotating wall must carry the net thrust, and a thrust bearing must be provided in both directions.
This invention is directed to a new and improved pump of the character described which employs floating, rotatable shrouds to reduce parasitic frictional drag as well as to allow the shrouds to be configured with lesser mass than might be required in order to support the pressure differential across the shrouds.